BUFFALO, N.Y. — A New York man who claims he struck a deal with Mark Zuckerberg in 2003 that entitles him to half of Facebook Inc. has included in a new court filing emails he said he exchanged with the Facebook founder.

In his federal court complaint, Paul Ceglia of Wellsville said the emails show, in part, how Zuckerberg tried to get him to abandon his interest in Facebook by souring their business relationship in 2004, while at the same time downplaying the popularity of the site following its launch at Harvard University, where Zuckerberg was a student.

Zuckerberg is accused in the complaint of breaching his contract with Ceglia by incorporating the website first known as thefacebook.com without telling him.

Ceglia seeks a 50 percent share of the company, which has more than 500 million users worldwide. Forbes magazine last month estimated Zuckerberg’s net worth at $13.5 billion.

Orin Snyder, an attorney for Facebook, called the claims “ridiculous.”

“This is a fraudulent lawsuit brought by a convicted felon and we look forward to defending it in court,” Snyder said.

Ceglia was placed on probation in 1997 after pleading guilty to possession of hallucinogenic mushrooms, Texas, court records show.

Ceglia’s amended filing in Buffalo on Monday came on the same day that a federal appeals court in San Francisco left in place a 2008 agreement settling a lawsuit by two former Harvard schoolmates of Zuckerberg who claimed he stole their idea to launch Facebook. The agreement called for Tyler and Cameron Winklevoss to receive a $20 million cash payment and a partial ownership of Facebook.